Messages in this thread | | | Date | Mon, 24 Feb 2020 21:20:14 +0800 | From | Feng Tang <> | Subject | Re: [LKP] Re: [perf/x86] 81ec3f3c4c: will-it-scale.per_process_ops -5.5% regression |
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On Mon, Feb 24, 2020 at 10:19:15AM +0800, Feng Tang wrote: > > > > > No, it's not the biggest, I tried another machine 'Xeon Phi(TM) CPU 7295', > > > which has 72C/288T, and the regression is not seen. This is the part > > > confusing me :) > > > > Hmm. > > > > Humor me - what happens if you turn off SMT on that Cascade Lake > > system? Maybe it's about the thread ID bit in the L1? Although again, > > I'd have expected things to get _worse_ if it's the two fields that > > are now in the same cachline thanks to alignment. > > I'll try it and report back.
I added "nosmt=force" on the 2S 4 nodes 96C/192T machine, and tested both 96 and 192 processes, and the regression still exists.
Also for Ying's suggestion about separate 'sigpending' to another cache line than '__refcount', it can not heal the regression either.
Thanks, Feng
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